Method of generating pilot pattern for adaptive channel estimation in ofdma systems, method of transmitting/receiving using the pilot pattern and apparatus thereof

ABSTRACT

Provided is a method of generating a pilot pattern capable of perform adaptive channel estimation, and a method and apparatus of a base station and a method and apparatus of a terminal using the pilot pattern. 
     The pilot pattern selects pilot symbol positions based on distances from pilots of previous orthogonal frequency division multiple access (OFDMA) symbols to a subcarrier position of a current OFDMA symbol in the frequency domain and the time domain, so that a low pilot density is maintained so as to effectively transmit data, and stable channel estimation performance can be obtained even in a bad channel environment. 
     In addition, the minimum burst allocation size is determined according to the channel environment between the base station and the terminal, guaranteeing channel estimation performance suitable for the channel environment, and improving granularity, channel estimation latency, and channel estimation memory size.

TECHNICAL FIELD

The present invention relates to a pilot pattern in a wirelesscommunication system, and more particularly, to a method of generating apilot pattern capable of minimizing channel estimation performancedegradation due to interpolation in a bad channel environment whilemaintaining a low pilot density, and a transmitting and receiving methodcapable of adaptively controlling channel estimation performance,granularity, channel estimation latency, channel estimation memory size,and the like, to be suitable for a channel environment between a basestation and a terminal, by using the generated pilot pattern.

BACKGROUND ART

In a wireless communication system, a received signal is influenced by achannel environment, and thus it is necessary to compensate for theinfluence of the channel environment. To do this, a predetermined pilotsymbol is inserted in the time domain and the frequency domain duringdata transmission between a transmitter and a receiver in the wirelesscommunication system. The receiver performs channel estimation using twocontinuous pilot symbols, to compensate for channel deterioration ofdata symbols between the two pilot symbols.

As a result, when the interval between the pilot symbols decreases, andthe density of the pilot symbols increases, the channel estimationperformance is improved. However, the ratio of the pilot symbols in aframe increases, which reduces information transmission efficiency.

FIGS. 1 and 2 show examples of a pilot pattern used in an existingorthogonal frequency-division multiplexing (OFDM) system.

FIG. 1 shows a pilot pattern used in a downlink partial usage ofsub-channels (PUSC) mode in IEEE 802.16e worldwide interoperability formicrowave access (WiMAX) standard, and FIG. 2 shows a pilot pattern usedin a European telecommunications standards institute (ETSI) digitalvideo broadcasting terrestrial (handheld) (DVB-T(H)) mode.

Referring to FIG. 1, in the pilot pattern, pilots are inserted intosubcarriers, which is repeated every 2 orthogonal frequency divisionmultiple access (OFDMA) symbols. In this structure, although sufficientOFDMA symbols are collected by the receiver to be used for channelestimation, a pilot interval is always fixed as 4 in a slot, so that inorder to compensate for the channel deterioration of a data subcarrierbetween the pilots, interpolation has to be performed, andcorrespondingly performance degradation due to the interpolation cannotbe avoided.

Referring to FIG. 2, in the pilot pattern, pilots are inserted intosubcarriers, which is repeated every 4 OFDM symbols. In this structure,although 4 OFDM symbols are collected to be used for channel estimation,the pilot interval is always fixed as 3, so that the channel estimationperformance degradation due to the interpolation cannot be avoidedeither.

In addition, the existing pilot pattern has a structure in whichadaptive control of the channel estimation performance, granularity,channel estimation latency, and the channel estimation memory sizeaccording to the channel environment is impossible.

Therefore, a pilot pattern capable of minimizing the channel estimationperformance degradation due to the interpolation while maintaining a lowpilot density, and an adaptive channel estimation method using the pilotpattern are required.

DETAILED DESCRIPTION OF THE INVENTION Technical Problem

The present invention provides a method of generating a pilot patterncapable of minimizing channel estimation performance degradation due tointerpolation in a bad channel environment while maintaining a low pilotdensity.

The present invention also provides a method of adaptively controlling achannel estimation performance, granularity, channel estimation latency,channel estimation memory size, and the like to be suitable for achannel environment between a base station and a terminal by using thegenerated pilot pattern.

The objects and advantages of the present invention will be explained inthe following description, which includes exemplary embodiments of thepresent invention. In addition, it can be easily understood that theobjects and advantages of the present invention can be implemented withmeans disclosed in the appended claims and combinations thereof.

Technical Solution

According to an aspect of the present invention, there is provided amethod of generating a pilot pattern, comprising: (a) determining a sizeof a slot which is a section in which a pilot pattern is repeated in thetime domain and the frequency domain; (b) determining an arbitrarysubcarrier in a first OFDMA (orthogonal frequency division multipleaccess) symbol within the slot in the time domain as a pilot insertingposition; (c) calculating frequency-time distances of each of remainingsubcarriers of a current OFDMA symbol after the first OFDMA symbolexcluding subcarriers into which pilots in all the previous OFDMAsymbols within the slot in the time domain are inserted, from the pilotsof all of the previous OFDMA symbols within the slot in the time domainto each of the remaining subcarriers; (d) comparing minimum distances ofthe frequency-time distance sets of the remaining subcarriers; and (e)determining a subcarrier having the largest frequency-time minimumdistance to be the pilot inserting position.

The method may further include, (f) when the number of the subcarriershaving the same largest value is two or more after comparing the lastminimum distances in the frequency-time distance sets, calculatingfrequency distances of each of the subcarriers having the same largestvalue, from the pilots of all of the previous OFDMA symbols within theslot in the time domain to each of the subcarriers having the samelargest value, in the frequency direction; (g) comparing minimumdistances in the frequency distance sets; and (h) determining thesubcarrier having the largest frequency minimum distance to be the pilotinserting position.

The method may further include, (i) when the number of subcarriershaving the same largest value is two or more after comparing the lastminimum distances in the frequency distance sets, determining anarbitrary one of the subcarriers having the same largest value of thelast minimum distances in the frequency distance sets to be the pilotinserting position.

According to an aspect of the present invention, there is provided atransmitting and receiving method for a base station, (a) determining aminimum burst allocation size of a terminal according to thepredetermined criterion; (b) generating a pilot pattern in which pilotintervals for channel estimation can be changed according to the minimumburst allocation size; and (c) generating a transmission signal based onthe pilot pattern.

The method may further include, (d) estimating a channel after channelestimation latency based on information on the determined uplink burstregion for a signal received from the terminal.

According to another aspect of the present invention, there is provideda transmitting and receiving method for a terminal, comprising: (a)receiving a signal transmitted according to a pilot pattern in whichpilot intervals for channel estimation can be changed, from a basestation; (b) detecting an up/downlink burst region from the receivedsignal; and (c) estimating a channel for the received signal afterchannel estimation latency based on information on the detected downlinkburst region.

The method may further include, (d) generating a pilot pattern in whichpilot intervals for channel estimation can be changed; and (e)generating a transmission signal according to the pilot pattern in theuplink burst region determined based on the information on the detecteduplink burst region.

According to another aspect of the present invention, there is providedan apparatus for generating a pilot pattern, comprising: a slotdeterminer determining the size of a slot which is a section in which apilot pattern is repeated in the time domain and the frequency domain; adistance calculator calculating frequency-time distances of each ofremaining subcarriers of a current OFDMA symbol after the first OFDMAsymbol excluding subcarriers into which pilots of previous OFDMA symbolswithin the slot in the time domain are inserted, from the pilots of theprevious OFDMA symbols within the slot in the time domain to each of theremaining subcarriers; a distance comparator comparing the minimumdistances of the frequency-time distance sets of the remainingsubcarriers; and a position determiner determining a subcarrier having amaximum frequency-time minimum distance to be the pilot insertingposition, and determining an arbitrary subcarrier in the first OFDMAsymbol within the slot in the time domain as the pilot insertingposition.

The distance calculator may calculate frequency distances of each of thesubcarriers having the same largest value, from the pilots of all of theprevious OFDMA symbols within the slot in the time domain to each of thesubcarriers having the same largest value, in the frequency direction,when the number of subcarriers having the same largest value is two ormore after comparing the last minimum distances in the frequency-timedistance sets, the distance comparator may compare the minimum distancesin the frequency distance sets, and the position determiner maydetermine the subcarrier having the largest frequency minimum distanceto be the pilot inserting position.

The position determiner may determine one of the subcarriers having thesame largest value of the last minimum distances in the frequencydistance sets to be the pilot inserting position, when the number ofsubcarriers having the same largest value is two or more after comparingthe last minimum distances in the frequency distance sets.

According to another aspect of the present invention, there is provideda transmitting and receiving apparatus of a base station, comprising: aburst determiner determining a minimum burst allocation size of aterminal according to the predetermined criterion; a pilot patterngenerator generating a pilot pattern in which pilot intervals forchannel estimation can be changed according to the minimum burstallocation size; and a transmission signal generator generating atransmission signal based on the pilot pattern.

The apparatus may further comprise a received signal processorestimating a channel after channel estimation latency based oninformation on the determined uplink burst region for a signal receivedfrom the terminal.

According to another aspect of the present invention, there is provideda transmitting and receiving apparatus of a terminal, comprising: asignal receiver receiving a signal transmitted according to a pilotpattern in which pilot intervals for channel estimation can be changed,from a base station; a burst region detector detecting an up/downlinkburst region from the received signal; a received signal processorestimating a channel for the received signal after channel estimationlatency based on information on the detected downlink burst region.

The apparatus may further comprise a pilot pattern generator generatinga pilot pattern in which pilot intervals for channel estimation can bechanged; and a transmission signal generator generating a transmissionsignal according to the pilot pattern in the uplink burst regiondetermined based on the information on the detected uplink burst region.

According to another aspect of the present invention, there is provideda computer readable recording medium having embodied thereon a computerprogram for executing a method of generating a pilot pattern, atransmitting and receiving method for a base station, and a transmittingand receiving method for a terminal.

Advantageous Effects

The pilot pattern selects pilot symbol positions based on distances frompilots of previous orthogonal frequency division multiple access (OFDMA)symbols to a subcarrier position of a current OFDMA symbol in thefrequency domain and the time domain, so that in the last OFDMA symbolin a slot, channel information at all pilot subcarrier positions iscopied and used for channel estimation. Therefore, a low pilot densitycan be maintained, allowing data to be transmitted effectively,preventing performance degradation due to interpolation in a badenvironment, and obtaining stable channel estimation performance.

In addition, channel estimation is performed by using the pilot pattern.

Therefore, the minimum burst allocation size is determined according tothe channel environment between the base station and the terminal,guaranteeing channel estimation performance suitable for the channelenvironment, and adaptively improving granularity, channel estimationlatency, and channel estimation memory size.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a pilot pattern used in a downlink partial usage ofsub-channels (PUSC) mode in IEEE 802.16e worldwide interoperability formicrowave access (WiMAX) standard.

FIG. 2 shows a pilot pattern used in a European telecommunicationsstandards institute (ETSI) digital video broadcasting terrestrial(handheld) (DVB-T (H)) mode.

FIG. 3 is a flowchart for explaining a method of generating a pilotpattern in a transmitter of an orthogonal frequency division multipleaccess (OFDMA) system according to an embodiment of the presentinvention.

FIGS. 4A to 4E are diagrams for explaining a pilot inserting order usedto generate the pilot pattern according to the embodiment shown in FIG.3.

FIG. 5A to 5D show examples of a pilot pattern for various slot lengthsgenerated by applying the method in FIG. 3.

FIG. 6 is a block diagram of an apparatus for generating a pilot patternaccording to an embodiment of the present invention.

FIG. 7 is a diagram for explaining an example of a channel environmentwhich becomes different according to terminal positions in a cell.

FIG. 8 is a diagram for explaining the number of OFDMA symbols which canbe selected in the pilot pattern generated according to an embodiment ofthe present invention for adaptive channel estimation according to achannel estimation of each terminal shown in FIG. 7 using overlappedpilot structures.

FIG. 9 shows the relationship between granularity, channel estimationlatency, channel estimation memory size, and a transmission channelenvironment of a terminal shown in FIG. 7.

FIG. 10 is a block diagram showing a signal processing flow between abase station A which selects an adaptive pilot pattern by using channelstate information and a user terminal B according to an embodiment ofthe present invention.

FIGS. 11A and 11B are flowcharts for explaining a method of transmittingand receiving data for a base station by determining a minimum burstallocation size according to an embodiment of the present invention.

FIGS. 12A and 12B are flowcharts for explaining a method of transmittingand receiving data for a terminal according to an embodiment of thepresent invention.

BEST MODE Mode of the Invention

Exemplary embodiments of the present invention will now be described indetail with reference to the attached drawings. Like reference numeralsdenote like elements in the drawings. In the description, the detaileddescription of widely known functions and structures may be omitted soas not to obscure the essence of the present invention.

In addition, when a part “comprises” a component, it means that the partmay further comprise other components, and does not exclude anycomponents unless otherwise described.

FIG. 3(FIG. 3A and FIG. 3B) is a flowchart for explaining a method ofgenerating a pilot pattern in a transmitter of an orthogonal frequencydivision multiple access (OFDMA) system according to an embodiment ofthe present invention.

The pilot pattern is a pattern for arranging pilot symbols in thefrequency domain and the time domain.

In an OFDM/OFDMA communication system, a burst is allocated to a dataframe according to a user, and according to the burst allocation size,the number of OFDMA symbols used for channel estimation is determined.In the pilot pattern according to the current embodiment, a pilotinterval in an OFDMA symbol used for channel estimation can be changedaccording to a minimum burst allocation size, so that by changing theminimum burst allocation size according to a channel environment,granularity, channel estimation latency, and channel estimation memorysize can be optimized, and stable channel estimation performance can beobtained.

Referring to FIG. 3, in order to form a pilot pattern, a slot size isdetermined (operation S301). According to the current embodiment, theslot is a section in which a pilot pattern is repeated in the timedomain and the frequency domain, and is defined by a frequency pilotinterval in which a pilot pattern is repeated in the frequency domainand a time pilot interval in which a pilot pattern are repeated in thetime domain. The size of the slot is represented as the number ofsubcarriers in the frequency domain and the number of OFDMA symbols inthe time domain within the slot, and can be selected according to thechannel characteristics of a target system.

It is determined that a current OFDMA symbol in which a pilot insertingposition is determined is a first OFDMA symbol of the slot (operationS302).

When the current OFDMA symbol is the first OFDMA symbol of the slot, anarbitrary subcarrier in the OFDMA symbol is determined to be the pilotinserting position (operation S303). A pilot position in each of theOFDMA symbols including the first OFDMA symbol is used as a referencefor determining a pilot position of the next OFDMA symbol.

For each OFDMA symbol from the second OFDMA symbol of the slot, thedistances from all the previous pilots to each of the current remainingsubcarriers, excluding subcarrier rows into which the pilots in theprevious OFDMA symbols of the slot are inserted, in frequency directionand time direction, are calculated. Thus, frequency-time distances areobtained (operation S304). Though a diagonal distance can also be used,the frequency-time distance, however, means the sum of each distance inthe frequency direction and the time direction. A weight factor isapplied to calculate each distance in the frequency direction and thetime direction, and may be different according to the system and theenvironment. The frequency-time distance is calculated using the one ofthe two continuous pilots, of the previous OFDMA symbol, which is closerto the current subcarrier.

The distance values in frequency-time distance sets calculated forremaining subcarriers are sequentially compared with each other, and thesubcarrier having the largest value is determined to be the pilotinserting position (operations S305 to S309).

For example, when four remaining subcarriers exist in the fourth OFDMAsymbol, each of the four remaining subcarriers has three frequency-timedistance values because frequency-time distances are calculated fromeach pilot of three previous (first, second, and third) OFDMA symbols. Aset of the three frequency-time distance values is referred to as thefrequency-time distance set, and four values which are the respectivesmallest values in the frequency-time distance sets of the foursubcarriers are referred to as a first minimum distance set. Next, fourvalues which are the respective second smallest values in thefrequency-time distance sets of the four subcarriers become a secondminimum distance set, and in this manner, a third minimum distance setis also constructed.

Returning to FIG. 3, values in the first minimum distance set of thefrequency-time distance sets are compared with each other (operationS305).

It is determined whether the number of subcarriers having the samelargest value (hereinafter, also referred to as maximum distance) in thefirst minimum distance set is two or more (operation S306).

When the number of subcarriers having the same maximum distance in thefirst minimum distance set is one, the one subcarrier is determined tobe the pilot inserting position (operation S307).

When the number of subcarriers having the maximum distance in the firstminimum distance set is two or more, it is determined whether the firstminimum distance set is the last minimum distance set to be compared inthe current OFDMA symbol (operation S308).

When the first minimum distance set is not the last minimum distanceset, for the subcarriers having the same maximum distance in the currentminimum distance set, values in the next minimum distance set arecompared with each other (operation S309), and the subcarrier having themaximum distance is determined to be the next pilot inserting position(operation S307).

When the number of subcarriers having the same maximum distance is stilltwo or more, even though values in the last minimum distance set havebeen compared, for each of the two or more subcarriers having the samemaximum distance, distances from pilots of previous OFDMA symbols toeach of the two or more subcarriers only in the frequency direction(hereinafter, referred to as frequency distances) are calculated(operation S310). Since a change in the frequency direction is fasterthan a change in the time direction, it is preferable that the distancesin the frequency direction are compared in order to select a properpilot position.

The frequency distances are compared with each other (operation S311),and the subcarrier having the largest frequency distance is determinedto be the pilot inserting position (operation S312). When the number offrequency distance values of each subcarrier is one or more, similarlyto operations S305 to 309, frequency distance values are sequentiallycompared with each other from the smallest one, and according to theresult of the comparison, the subcarrier having the largest value(hereinafter, also referred to as the maximum frequency distance) isdetermined to be the pilot inserting position.

For example, in the fourth OFDMA symbol, when the number of remainingsubcarriers having the same maximum distance in the last minimumdistance set of the frequency-time sets is two, each of the tworemaining subcarriers has three frequency distance values becausefrequency distances are calculated from pilots of three (first, second,and third) previous OFDMA symbols to each of the remaining subcarriers.A set of the three frequency distance values is referred to as afrequency distance set, and two values selected as the respectivesmallest values in the frequency distance sets of two subcarriers arereferred to as a first frequency minimum distance set. Next, two valuesselected as the respective second smallest values in the frequencydistance sets of the two subcarriers are referred to as a secondfrequency minimum distance set, and similarly, a third frequency minimumdistance set is also constructed.

Returning to FIG. 3, when the number of subcarriers having the samelargest value is two or more, even though values in the last minimumdistance set of the frequency distance sets have been compared, theposition of an arbitrary one of the subcarriers having the same largestvalue is determined to be the pilot inserting position (operation S313).

It is determined whether the current OFDMA symbol is the last OFDMAsymbol in the slot (operation S314).

When the current OFDMA is not the last OFDMA symbol, in order todetermine the pilot inserting position for the next OFDMA symbol byperforming operations 304 to 313, an OFDMA symbol index is increased by1 (operation S315). Operations 304 to 313 are repeated till the lastOFDMA symbol within the slot.

A pilot inserted into each OFDMA symbol of the slot which has the samesize in the frequency domain and the time domain, that is, the slothaving equal frequency pilot interval and time pilot interval, in thefrequency domain, is repeatedly positioned every interval which is thesame as the time pilot interval.

FIGS. 4A to 4E are diagrams for explaining a pilot inserting order usedto generate the pilot pattern according to the embodiment shown in FIG.3.

For convenience of description, the case where a slot including fivesubcarriers, that is, first (a-th) to fifth (e-th) subcarriers in thefrequency domain, and five OFDMA symbols, that is, first (m-th) to fifth(q-th) OFDMA symbols in the time domain, has a slot size of 5 is used asan example. It will be understood by those skilled in the art that themethod can be applied to a case where the slot size in the frequencydomain is different from that in the time domain, or the slot size issmaller or larger than 5.

Referring to FIG. 4A, a first pilot is inserted into an a-th subcarrier,which is an arbitrary subcarrier in the m-th OFDMA symbol that is thefirst OFDMA symbol of the slot. The pilot is repeatedly inserted intothe m-th OFDMA symbol at an interval of 5.

Referring to FIG. 4B, in an n-th OFDMA symbol, which is the second OFDMAsymbol, b, c, d, and e-th subcarriers, but not the a-th subcarrier rowinto which the pilot of the m-th OFDMA symbol is inserted, becomecandidate positions into which a second pilot is to be inserted.

The frequency-time distance from the a-th subcarrier in the m-th OFDMAsymbol that is the previous pilot position to the b-th subcarrier in then-th OFDMA symbol is 2, calculated by adding a distance of 1 in thefrequency domain to a distance of 1 in the time domain. In this manner,frequency-time distances from the a-th subcarrier in the m-th OFDMAsymbol that is the previous pilot position to the c, d, and e-thsubcarriers are respectively 3, 3, and 2. The frequency-time distancesto the d- and e-th subcarrier in the n-th OFDMA symbol are calculatedusing a lower pilot which is closer to the d- and e-th subcarrier thanan upper pilot in the m-th OFDMA symbol. In the above example, a weightfactor of 1 is applied to calculate each distance in the frequencydirection and the time direction. However, as described above, adifferent weight factor to the direction can be applied according to thesystem and the environment.

Therefore, frequency-time distance sets calculated at the b, c, d, and esubcarriers in the n-th OFDMA symbol are (2), (3), (3), and (2), andsince the number of frequency-time distances of each subcarrier is 1,the minimum distance set is {2, 3, 3, 2}.

The subcarriers having the largest value in the minimum distance set,that is, having the maximum distance, are the c and d-th subcarriers,having the distance of 3. Since the maximum distances of the c and d-thsubcarriers are both 3, and there is no further minimum distance set tobe compared, distances are calculated only in the frequency domain fromthe positions of the c and d-th subcarriers to the previous pilot (thea-th subcarrier in the m-th OFDMA symbol, or a subcarrier distant fromthe a-th subcarrier in the m-th OFDMA symbol by the frequency pilotinterval) and are compared with each other.

Here, the frequency distances are both 2, so one of the c and d-thsubcarriers is arbitrarily selected as a subcarrier into which the pilotis inserted. In the example of FIG. 4B, the c-th subcarrier in the n-thOFDMA symbol is selected as the pilot position.

Referring to FIG. 4C, in the o-th OFDMA symbol that is the third OFDMAsymbol, the b, d, and e-th subcarriers but not the a and c-th subcarrierrows into which the pilots of the m and n-th OFDMA symbols that areprevious symbols are inserted, become candidate positions into which athird pilot is to be inserted.

Frequency-time distances from the pilot position of each of the m andn-th OFDMA symbols to the b, d, and e-th subcarriers in the o-th OFDMAsymbol are sequentially calculated as (3,2), (4,2), and (3,3). The firstminimum distance set is {2, 2, 3}, wherein 2 is selected as the smallestof the distances (3,2) of the b-th subcarrier, 2 is selected as thesmallest of the distances (4,2) of the d-th subcarrier, and 3 isselected as the smallest value of distances (3,3) of the e-thsubcarrier. In the first minimum distance set, the maximum distance is3, of the e-th subcarrier. Accordingly, the pilot inserting position inthe o-th OFDMA symbol is the e-th subcarrier.

Referring to FIG. 4D, in the p-th OFDMA symbol, that is the fourth OFDMAsymbol, the b and d-th subcarriers, but not the a, c, and e-thsubcarrier rows into which the pilots of the m, n, and o-th OFDMAsymbols that are previous symbols are inserted, become candidatepositions into which a fourth pilot is to be inserted.

Frequency-time distances from the pilot position of each of the m, n,and o-th OFDMA symbols to the b and d-th subcarriers in the p-th OFDMAsymbol are sequentially calculated as (4,3,3) and (5,3,2). The firstminimum distance set is {2,3}, wherein 3 is selected as the smallest ofthe distances (4,3,3) of the b-th subcarrier, and 2 is selected as thesmallest value of distances (5,3,2) of the d-th subcarrier. In the firstminimum distance set, the maximum distance is 3, of the b-th subcarrier.Accordingly, the pilot inserting position in the p-th OFDMA symbol isthe b-th subcarrier.

Referring to FIG. 4E, in the q-th OFDMA symbol, which is the fifth andlast OFDMA symbol in the slot, the last pilot inserting position is theonly remaining d-th subcarrier.

When it is assumed that the channel environment does not significantlychange during a slot, the pilot symbols of previous OFDMA symbols can beused for the last OFDMA symbol. Therefore, channel information can becopied from the positions of all of the pilot subcarriers to be used forchannel estimation, preventing performance degradation due tointerpolation. Since the channel information can be copied from thepositions of all the pilot subcarriers in the last OFDMA symbol, thelargest pilot interval is always 1.

FIG. 5A to 5D show examples of a pilot pattern for various slot lengthsgenerated by applying the method in FIG. 3.

In each of FIGS. 5A to 5D, the numbers in each of the subcarriersequentially show frequency-time distances from pilots of previous OFDMAsymbols including a pilot of a first OFDMA symbol to each subcarrier ofa current OFDMA symbol. The leftmost number is the frequency-timedistance from the pilot of the first OFDMA symbol in the slot to thecurrent subcarrier position, and the rightmost number is thefrequency-time distance from the pilot of the preceding OFDMA symbol tothe current subcarrier position.

FIG. 5A shows a pilot pattern having a slot size of 2, with pilotsinserted in zigzags. In this structure, the pilot density is very high,so this pattern is preferably used as a preamble structure of a framerather than a repeated pilot pattern.

FIG. 5B shows a pilot pattern having a slot size of 7. When 4 OFDMAsymbols are used for channel estimation, the pilot interval does notexceed 3, and when 7 OFDMA symbols are used, which is the same number asthe slot size, the pilot interval can be 1, allowing stable channelestimation performance without an interpolation.

The pilot patterns shown in FIGS. 1 and 5B have the same pilot density.However, although in FIG. 1, two or more OFDMA symbols are used forchannel estimation, the pilot interval cannot be decreased to less than4. Therefore, channel estimation performance degradation in a badchannel environment cannot be avoided.

FIG. 5C shows a pilot pattern having a slot size of 8. In this case,when the number of OFDMA symbols used for channel estimation is 1, 2, 4,or 8, a regular interval pilot pattern can be obtained, allowing stablechannel estimation performance without an interpolation.

FIG. 5D shows a pilot pattern having a slot size of 12. When 4 OFDMAsymbols are used, the pilot interval does not exceed 4, and when 12OFDMA symbols are used, which is the same number as the slot size, thepilot interval can be 1, allowing stable channel estimation performancecan be obtained without an interpolation.

The pilot patterns shown in FIGS. 2 and 5D have the same pilot density.However, although in FIG. 2, four or more OFDMA symbols are used forchannel estimation, the pilot interval cannot be decreased to less than3. Therefore, channel estimation performance degradation in a badchannel environment cannot be avoided.

FIG. 6 is a block diagram of an apparatus for generating a pilot patternaccording to an embodiment of the present invention. Redundantdescription with the above description will be omitted in the followingdescription.

Referring to FIG. 6, the apparatus for generating a pilot patternincludes a slot determiner 610, a distance calculator 620, a distancecomparator 630, and a position determiner 640.

The slot determiner 610 determines the size of a slot, which is asection in which a pilot pattern is repeated in the frequency domain andthe time domain. The size of the slot may be selected according to thechannel characteristics of a target system.

The distance calculator 620 calculates frequency-time distances frompilots of previous OFDMA symbols to each of remaining subcarriersexcluding subcarriers into which pilots in the previous OFDMA symbols ofthe slot are inserted, for each OFDMA symbol after the first OFDMAsymbol of the slot. The frequency-time distance is the sum of thedistances from the pilots of the previous OFDMA symbols to a subcarrierin the frequency axis and the time axis. When the distance comparator630 compares values in the last minimum distance set of frequency-timedistance sets, and the number of subcarriers having the same maximumminimum distance is two or more, the distance calculator 620 calculatesfrequency distances only in the frequency direction from the pilots ofthe previous OFDMA symbols to each of the two or more subcarriers.

The distance comparator 630 sequentially compares the minimum distances(ranging from the first minimum distance to the last minimum distance)in the frequency-time distance sets of each of remaining subcarriers,until a single subcarrier having the maximum frequency-time minimumdistance is selected. For the distance comparison, the comparison ofnext frequency-time minimum distances is performed on subcarriers havingthe same largest value of current frequency-time minimum distances. Whenthe number of subcarriers having the same maximum minimum distance istwo or more, even though the last minimum distances of thefrequency-time sets have been compared with each other, the distancecomparator 630 compares frequency distances calculated by the distancecalculator 620. The frequency distance comparison is sequentiallyperformed on from the smallest distances of the frequency distance sets,and the comparison of the next frequency minimum distances is performedon subcarriers having the same largest value of current frequencyminimum distances.

The position determiner 640 determines an arbitrary subcarrier positionin a first OFDMA symbol within a slot as a pilot inserting position, andfrom the second OFDMA symbol, determines the subcarrier having themaximum frequency-time minimum distance as the pilot inserting position.When the number of subcarriers having the same maximum frequency-timeminimum distance is two or more, even though the last minimum distancesin the frequency-time distance sets have been compared with each other,the position determiner 640 determines the subcarrier having the maximumfrequency distance as the pilot inserting position. Thereafter, when thenumber of subcarriers having the same maximum last frequency minimumdistance is two or more, an arbitrary one of the two or more subcarriersis determined to be the pilot inserting position.

FIGS. 7 to 10 show examples of adaptively applying a pilot patterndesigned according to an embodiment of the present invention, accordingto a channel environment between a base station and a terminal in anOFDMA system.

Factors to be considered when the pilot pattern in the OFDMA system isdesigned are mainly granularity, pilot density, transmission efficiency,channel estimation latency, memory size needed for channel estimation,and channel estimation performance. Granularity is a characteristicrequired to effectively support burst data having a small size used forvoice over Internet protocol services or the like. Pilot density is acharacteristic that the ratio of pilot subcarriers to data subcarriersmust low to obtain high transmission efficiency. The channel estimationlatency represents the number of OFDMA symbols which have to be receivedfor collecting channel information from pilots needed for channelestimation while maintaining a low pilot density. As the channelestimation latency increases, the memory size for storing the past dataneeded for channel estimation also increases. The channel estimationperformance becomes stable as channel information on pilots is usedmore. However, if the number of pilots is insufficient, interpolationhas to be performed at a data subcarrier position between pilotsubcarriers. These requirements cannot be simultaneously satisfied.However, by using tolerance of the channel estimation performanceaccording to the channel environment, other types of performance can beadaptively improved.

FIG. 7 is a diagram for explaining an example of a channel environmentwhich changes according to terminal positions in a cell.

A type I terminal is located near a base station and therefore has avery good channel environment with high signal strength and frequentline-of-sight signals. A type II terminal is a little further than thetype 1 terminal from the base station, and therefore has a relativelygood channel environment, but suffers some multipath influence. A typeIII terminal is a little further than the type II terminal from the basestation, and therefore has a bad channel environment and suffers fromserious multipath influence. A type IV terminal is at the edge of thecell and therefore has a very bad channel environment with almost noline-of-sight signals, very low signal strength, and seriousinterference from adjacent cells and multipath influence.

The above examples describe four types of channel environment. However,it will be understood by those skilled in the art that the types maydiffer according to circumstance.

FIG. 8 is a diagram for explaining the number of OFDMA symbols which canbe selected from the pilot pattern generated according to an embodimentof the present invention for adaptive channel estimation according to achannel estimation of each terminal shown in FIG. 7, using overlappedpilot structure.

In the above example, the size of a slot includes 8 subcarriers in thefrequency domain and 8 OFDMA symbols in the time domain, a numeral in asubcarrier in each OFDMA symbol represents the order of the subcarrierposition determined to be a pilot inserting position in each OFDMAsymbol.

Referring to FIG. 8, the pilot pattern according to the currentembodiment can change the pilot symbol density (the frequency pilotinterval used for channel estimation) according to the channelenvironment. When the channel environment is good, the minimum burstallocation unit (size) is small. Therefore channel estimation latency atthe receiver decreases, and the frequency pilot interval used forchannel estimation increases.

The type I terminal has a good channel environment, so the minimum burstallocation size is 1 OFDMA symbol, and therefore the frequency pilotinterval for channel estimation becomes 8.

The type II terminal has a relatively good channel environment, so theminimum burst allocation size is 2 OFDMA symbols, and therefore thefrequency pilot interval for channel estimation becomes 4.

The type III terminal has a bad channel environment, so the minimumburst allocation size is 4 OFDMA symbols, and therefore the frequencypilot interval for channel estimation becomes 2.

The type IV terminal has a very bad channel environment, so the minimumburst allocation size is 8 OFDMA symbols, and therefore the frequencypilot interval for channel estimation becomes 1.

The pilot structures according to the minimum burst allocation sizesallocated to the type I, II, III, and IV terminals may change accordingto pilot patterns and the channel environment of the terminal. However,since the channel estimation performance is determined by the pilotsubcarrier interval, it is preferable that a structure having a regularpilot interval is selected. When the pilot interval is not regular, themaximum pilot interval becomes a critical factor in the channelestimation performance.

FIG. 9 shows the relationship between granularity, channel estimationlatency, and channel estimation memory size according to a transmissionchannel environment of a terminal shown in FIG. 7.

Since the type I terminal has a very good channel environment, stablechannel estimation performance can be obtained by using the pilotstructure corresponding to the type I position shown in FIG. 8.Therefore, the type I terminal performs channel estimation using asingle OFDMA symbol, so that the burst size to be allocated is small,channel estimation latency and memory size are small, and granularity isexcellent.

Since the type II terminal has a relatively good channel environment,stable channel estimation performance can be obtained by using the pilotstructure corresponding to the type II position shown in FIG. 8.Therefore, the type II terminal performs the channel estimation usingtwo OFDMA symbols, giving still excellent granularity, low channelestimation latency, and low memory size.

Since the type III terminal has a relatively bad channel environment,stable channel estimation performance can be obtained by using the pilotstructure corresponding to the type Ill position shown in FIG. 8.Therefore, the type III terminal performs the channel estimation usingfour OFDMA symbols, deteriorating granularity and increasing the channelestimation latency and memory size.

Since the type IV has a very bad channel environment, stable channelestimation performance has to be guaranteed by using the pilot structurecorresponding to the type IV position shown in FIG. 8. Therefore, 8OFDMA symbols in the slot are used to perform channel estimation,deteriorating granularity and increasing the channel estimation latencyand memory size. However, channel information from pilot subcarriers ofother OFDMA symbols can be copied to be used for all subcarriers in thelast OFDMA symbol of the slot, preventing channel estimation performancedegradation due to interpolation. Assuming that the channel does notsignificantly change in the time domain during a slot, the pilot channelinformation on previous OFDMA symbols in the slot can be copied to thelast OFDMA symbol in the slot.

FIG. 10 is a block diagram showing a signal processing flow between abase station A which selects an adaptive pilot pattern by using channelstate information and a user terminal B according to an embodiment ofthe present invention.

The pilot pattern generated according to the current embodiment of thepresent invention can adaptively select a pilot structure that can beused for channel estimation according to the channel environment betweenthe base station and the terminal, allowing efficient application ofresources.

FIG. 10 shows i) a flow in which a base station A determines a minimumburst allocation unit (size) of a user terminal B using feedback channelstate information received from the user terminal B or channel statedetermination criterion algorithm set of the base station A itself inadvance, and transmits a signal to the user terminal B, and the userterminal B detects the minimum burst allocation size in the signalreceived from the base station A and performs channel estimation, andii) a flow in which the user terminal B transmits a signal to the basestation A based on the detected minimum burst allocation size, and thebase station A processes the signal received from the user terminal Bbased on the minimum burst allocation size allocated to the userterminal B in advance and performs channel estimation.

Referring to FIG. 10, the base station A includes a transmitter and areceiver. The transmitter includes a burst region determiner 1000, atransmission signal generator 1010, a pilot pattern generator 1020, anda signal transmitter 1030. The receiver includes a signal receiver 1040and a received signal processor 1050. The user terminal B includes atransmitter and a receiver. The transmitter includes a transmissionsignal generator 1090, a pilot pattern generator 1103, and a signaltransmitter 1100. The receiver includes a signal receiver 1060, areceived signal processor 1070, and a burst region detector 1080.

In the transmitter of the base station A, the burst determiner 1000determines the minimum burst allocation size of the terminal based on adetermination criterion set in advance. The determination criterion maybe the channel state information received from the terminal or a channelstate determination criterion algorithm set in the base station itselfin advance. The burst determiner 1000 determines the minimum burstallocation size to be small as the channel state allows. The burstdeterminer 1000 includes a channel environment determiner 1001 fordetermining the channel environment based on the determinationcriterion, a minimum burst allocation size determiner 1003 fordetermining the minimum burst allocation size of the terminal based onthe channel environment, and an up/downlink burst region determiner 1005for determining an up and down link burst region including informationon the minimum burst allocation size. The channel environment may be setto include position information on the terminal with respect to the basestation. The minimum burst allocation size of the terminal is from a 1OFDMA symbol to the number of OFDMA symbols of a slot, a slot size inthe time domain.

In the transmission signal generator 1010, a frame encoder 1011 encodesthe information on the up/downlink burst region determined by the burstdeterminer 1000, into a frame header. A baseband processor 1013 includessuch as a serial to parallel converter, an inverse fast Fouriertransformer, a cyclic prefix (CP) inserting unit, and a parallel toserial converter, and inserts a data symbol and a pilot symbol into asignal output from the frame encoder 1011 according to a control signalof the pilot pattern generator 1020, to perform OFDMA modulation.

In the signal transmitter 1030, a digital to analog (D/A) converter 1031converts a digital signal output from the transmission signal generator1010 into an analog signal, and a wireless transmitter (also referred toas radio frequency (RF) front-end) 1033 up-converts the analog signalinto an RF signal and transmits the RF signal.

The pilot pattern generator 1020 generates a pilot pattern in which apilot interval used for channel estimation can be changed according tothe minimum burst allocation size, and generates a signal forcontrolling the position of a pilot to be inserted according to thepilot pattern. The pilot pattern is generated according to theembodiments of the present invention, by determining pilot positions ineach OFDMA symbol within a slot which is a section in which pilots arerepeated in the time domain and the frequency domain, based on distancesin the frequency and time direction, from pilot positions in theprevious OFDMA symbols within the slot to a subcarrier in a currentOFDMA symbol excluding rows of subcarriers into which the pilots of theprevious OFDMA symbols are inserted. The pilot pattern generated by thepilot pattern generator 1020 may be as described above with reference toFIGS. 3 to 5, so their detailed description will be omitted.

In the receiver of the base station A, the signal receiver 1040 receivesa signal from the user terminal B, a radio receiver 1041 down-convertsan RF signal into an intermediate frequency (IF) signal, and an analogto digital (ND) converter 1043 converts an analog signal into a digitalsignal. In the received signal processor 1050, a baseband processor 1051demodulates the converted digital signal based on an uplink burst regiondetermined by the burst determiner 1000, and a frame decoder 1053recovers the received signal by performing frame decoding. The basebandprocessor 1051 includes such as a serial to parallel converter, a fastFourier transformer, and a parallel to serial converter, and demodulatesdata received after channel estimation latency according to the uplinkminimum burst size, and estimates a channel.

In the receiver of the user terminal B, the signal receiver 1060receives a signal from the base station A through a wireless channel. Inthe signal receiver 1060, a radio receiver (also referred to as an RFfront-end) 1061 down-converts the RF signal into the IF signal, and anND converter 1063 converts the analog signal into the digital signal.The signal received from the base station A is a signal transmittedaccording to a pilot pattern in which pilot intervals used for thechannel estimation can be changed. The pilot pattern is generatedaccording to the embodiments of the present invention, by determiningpilot positions in each OFDMA symbol of a slot which is a section inwhich pilots are repeated in the time domain and the frequency domain,based on distances in the frequency and time direction, from pilotpositions in the previous OFDMA symbols within the slot to a subcarrierin a current OFDMA symbol excluding rows of subcarriers into which thepilots in the previous OFDMA symbols are inserted.

In the received signal processor 1070, a baseband processor 1071demodulates the received signal, and a frame decoder 1073 recovers thereceived signal by performing frame decoding. A baseband processor 1071includes such as a serial to parallel converter, a fast Fouriertransformer, and a parallel to serial converter, and demodulates datareceived after channel estimation latency according to a downlinkminimum burst size detected by a burst region detector 1080 which willbe described later, and estimates a channel.

In the burst region detector 1080, a downlink burst region detector 1081detects the downlink burst region based on the information recoveredfrom the frame header of the received signal, and an uplink burst regiondetector 1083 detects an uplink burst region.

The transmitter of the user terminal B transmits data to the basestation A according to the minimum burst allocation size correspondingto detected information on the uplink burst region. In the transmissionsignal generator 1090, a frame encoder 1091 encodes detected uplinkburst region information including the minimum burst allocation sizeinto a frame header, and a baseband processor 1093 inserts pilotsaccording to a control signal of the pilot pattern generator 1103. Thebaseband processor 1093 generates a pilot pattern in which pilotintervals for channel estimation can be changed, in order to generate atransmission signal, and includes a serial to parallel converter, aninverse fast Fourier transformer, a cyclic prefix (CP) inserting unit,and a parallel to serial converter to perform OFDMA modulation on datato be transmitted. In the signal transmitter 1100, a D/A converter 1101converts a digital signal output from the transmission signal generator1090 into an analog signal, and a radio transmitter (also referred to asan RF front-end) 1105 up-converts the analog signal into an RF signaland transmits the RF signal.

FIGS. 11A and 11B are flowcharts for explaining a method of transmittingand receiving data from a viewpoint of a base station according to theembodiment shown in FIG. 10, and FIGS. 12A and 12B are flowcharts forexplaining a method of transmitting and receiving data from a viewpointof a user terminal. Redundant description with the above descriptionwill be omitted in the following description.

Referring to FIG. 11A, the base station determines the minimum burstallocation size of the terminal based on a determination criterion setin advance. For example, the base station may determine the minimumburst allocation size based on channel state information received fromthe terminal (operation S1110) or the channel state determinationcriterion algorithm set of the base station itself in advance.

The base station determines a channel environment based on the receivedchannel state information (operation S1115), determines the minimumburst allocation size of the terminal based on the channel environment(operation S1120), and determines an up/downlink burst region includingthe minimum burst allocation size information (operation S1125). Thechannel environment can be set using parameters such as the distance ofthe terminal from the base station. When the channel environment betweenthe terminal and the base station is good, the minimum burst allocationsize is small. The minimum burst allocation size of the time domain isin the range between 1 OFDMA symbol and a slot size in the time domain.As the minimum burst allocation size decreases, a frequency pilotinterval for channel estimation increases.

Next, a transmission signal is generated based on the pilot patterngenerated according to the current embodiment of the present invention,and transmitted to the terminal (operation S1130).

Referring to FIG. 12A, the terminal receives the signal transmittedaccording to the pilot pattern from the base station (operation S1210).

The terminal detects the up/downlink burst region from a frame header ofthe received signal (operation S1215).

A channel for the received signal is estimated based on the detecteddownlink burst region after channel estimation latency (operationS1220).

Referring to FIG. 12B, the terminal checks and uses an uplink burstregion of data to be transmitted based on the detected uplink burstregion information (operation S1250), and generates a pilot pattern inwhich pilot intervals for channel estimation can be changed.

A transmission signal is generated in the determined uplink burst regionbased on the pilot pattern (operation S1255).

Referring to FIG. 11B, the base station receives the signal from theterminal (operation S1150).

The base station estimates a channel based on the uplink burst regiondetermined according to the channel environment when transmitting asignal to the terminal after channel estimation latency in response tothe received signal (operation S1155).

In the pilot pattern in which pilot intervals for channel estimation canbe changed, each OFDMA symbol brings pilot information on the previousOFDMA symbols, so that all subcarriers in the last OFDMA symbol in aslot can use pilot information without interpolation. Therefore, thepilot interval can be determined according to the positions of OFDMAsymbols in the slot. Accordingly, a proper pilot structure can beselected according to the channel environment. Detailed description isprovided with reference to FIGS. 3 to 9.

For convenience of description, an OFDMA system has been used as anexample. However, it will be understood by those skilled in the art thatthe present invention can also be applied to an OFDM system.

This application claims the benefit of United States Patent ApplicationNo. 10-2007-0040013, filed on Apr. 24, 2007 in the Korean IntellectualProperty Office, and the benefit of U.S. Provisional Patent ApplicationNo. 60/794,328, filed on Apr. 24, 2006, and U.S. Patent No. 60/845,571,filed on Sep. 19, 2006, the disclosures of which are incorporated hereinin their entirety by reference.

The invention can also be embodied as computer readable code on acomputer readable recording medium. The computer readable recordingmedium is any data storage device that can store data which can bethereafter read by a computer system. Examples of the computer readablerecording medium include read-only memory (ROM), random-access memory(RAM), CD-ROMs, magnetic tapes, floppy disks, optical data storagedevices, and carrier waves (such as data transmission through theInternet). The computer readable recording medium can also bedistributed over network coupled computer systems so that the computerreadable code is stored and executed in a distributed fashion. Also,functional programs, code, and code segments for accomplishing thepresent invention can be easily construed by programmers skilled in theart to which the present invention pertains.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those skilled in the art that various changes in form and detail maybe made therein without departing from the spirit and scope of theinvention as defined by the appended claims. The exemplary embodimentsshould be considered in a descriptive sense only, and not for purposesof limitation. Therefore, the scope of the invention is defined not bythe detailed description of the invention but by the appended claims,and all differences within the scope will be construed as being includedin the present invention.

1. A transmitting and receiving method for a terminal, comprising: (a) receiving a signal transmitted according to a pilot pattern in which pilot intervals for channel estimation can be changed, from a base station; (b) detecting an up/downlink burst region from the received signal; (c) estimating a channel for the received signal after channel estimation latency based on information on the detected downlink burst region.
 2. The method of claim 1, wherein (b) comprises detecting the up/downlink burst region from a frame header of the received signal.
 3. The method of claim 2, further comprising: (d) generating a pilot pattern in which pilot intervals for channel estimation can be changed; and (e) generating a transmission signal according to the pilot pattern in the uplink burst region determined based on the information on the detected uplink burst region.
 4. The method of claim 3, wherein the pilot pattern is generated by determining pilot positions of each OFDMA symbol within a slot which is a section in which the pilot pattern is repeated in the time domain and the frequency domain, based on distances from pilot positions of previous OFDMA symbols of the slot to each subcarrier of a current OFDMA symbol excluding subcarriers into which the pilots of the previous OFDMA symbols are inserted, in the time direction and the frequency direction.
 5. A transmitting and receiving apparatus of a terminal, comprising: a signal receiver receiving a signal transmitted according to a pilot pattern in which pilot intervals for channel estimation can be changed, from a base station; a burst region detector detecting an up and down link burst region from the received signal; a received signal processor estimating a channel for the received signal after channel estimation latency based on information on the detected downlink burst region.
 6. The apparatus of claim 5, wherein the burst region detector detects the up and down link burst region from a frame header of the received signal.
 7. The apparatus of claim 6, further comprising: a pilot pattern generator generating a pilot pattern in which pilot intervals for channel estimation can be changed; and a transmission signal generator generating a transmission signal according to the pilot pattern in the uplink burst region determined based on the information on the detected uplink burst region.
 8. The method of claim 7, wherein the pilot pattern is generated by determining pilot positions of each OFDMA symbol within a slot which is a section in which a pilot pattern is repeated in the time domain and the frequency domain, based on distances from pilot positions of previous OFDMA symbols of the slot to each subcarrier of a current OFDMA symbol excluding subcarriers into which the pilots of the previous OFDMA symbols are inserted, in the time direction and the frequency direction. 